FIG. 1 shows a schematic representation of the essential features of a typical prior-art fiber optic transceiver. The main circuit 1 contains at a minimum transmit and receiver circuit paths and power 19 and ground connections 18. The receiver circuit typically consists of a Receiver Optical Subassembly (ROSA) 2 which contains a mechanical fiber receptacle as well as a photodiode and pre-amplifier (preamp) circuit. The ROSA is in turn connected to a post-amplifier (postamp) integrated circuit 4, the function of which is to generate a fixed amplitude digital signal that is connected to outside circuitry via the RX+ and RX−pins 17. The postamp circuit also often provides a digital output signal known as Signal Detect or Loss of Signal indicating the presence or absence of suitably strong optical input. The Signal Detect output is provided as an output on pin 20. The transmit circuit will typically consist of a Transmitter Optical Subassembly (TOSA) 3 and a laser driver integrated circuit 5. The TOSA contains a mechanical fiber receptacle as well as a laser diode or LED. The laser driver circuit 5 will typically provide AC drive and DC bias current to the laser. The signal inputs for the driver are obtained from the TX+ and TX−pins 12. Typically, the laser driver circuitry will require individual factory setup of certain parameters such as the bias current (or output power) level and AC modulation drive to the laser. Typically, this is accomplished by adjusting variable resistors or placing factory selected resistors 7, 9 (i.e., having factory selected resistance values). Additionally, temperature compensation of the bias current and modulation is often required. This function can be integrated in the laser driver integrated circuit or accomplished through the use of external temperature sensitive elements such as thermistors 6, 8.
The TX disable pin 13 allows the transmitter to be shut off by the host device, while the TX fault pin 14 is an indicator to the host device of some fault condition existing in the laser or associated laser driver circuit. In addition, the optoelectronic device 1 may include an optional eye-safety integrated circuit 11 that performs functions aimed at preventing non-eyesafe emission levels when a fault condition exists in the laser circuit. Also shown in FIG. 1 is an EEPROM 10 for storing standardized serial ID information that can be read out via a serial interface (e.g., using the serial interface of the ATMEL AT24C01A family of EEPROM products) consisting of a clock 15 and data 16 line.
The signal pins described above collectively provide an electrical interface between the optoelectronic device 1 and the host device. The optoelectronic transceiver industry over the years has standardized one such interface, known as the GBIC standard. An advantage of the GBIC standard is its relative simplicity and the low production cost of the integrated circuits required for implementation. Another advantage is that the size of the transceiver can be quite compact.
One disadvantage of the GBIC standard, however, is that the transceiver is reliant on the host device to perform a variety of operations such as reset and shutdown. If the host device malfunctions, the transceiver attached to it may not be able to perform these operations properly. Another disadvantage of the GBIC standard is its inflexibility. It is difficult to implement functionality in addition to those described in the GBIC standard.
Accordingly, there is a need for a highly flexible interface between an optoelectronic device and a host device.